1. Field of the Invention
The present invention relates to a novel lacquer composition based on special, olefinically unsaturated polyester resins which may be radially cured at temperatures of below 80.degree. C. and to their use for coating substrates, in particular wood.
2. Description of the Prior Art
The binders based on unsaturated polyester resins which are customarily used for radially curable coatings generally contain styrene as a copolymerizable monomer. Styrene evaporates during processing resulting in costly purification of the air in production shops and the exhaust air from drying units.
DE-AS 2,221,335 describes UV-light curable, unsaturated polyester resins, which do not contain styrene, as binders for coating compositions. They are, however, used in film thicknesses of less than 50 .mu.m. Greater film thicknesses considerably lengthen drying times, particularly if the coatings are to be cured with peroxides.
Unsaturated polyester resins that have a similar structure and do not contain monomers are known from DE-OS 3,900,257. However, because the drying time of these products, which act as binders for coating compositions, is excessively long at room temperature, they must be cured by infrared irradiation.
Systems containing styrene frequently contain paraffin as a drying accelerator. During radial curing, this paraffin floods to prevent the disruptive influence of atmospheric oxygen. It has been shown that monomer-free binders according to DE-OS 3,900,257 to which paraffin was added, have very long drying times. After curing, the resultant lacquer films have both poor polishability and a surface with poor flow-out.
An object of the present invention is to provide a novel coating composition based on polyester resins that do not contain styrene, which may be rapidly cured by free radical polymerization to give hard, readily sandable and polishable surfaces without poor flow-out.
This object may be achieved with the coating compositions according to the invention which are described in greater detail below.